Root mounting for rotor blades



1942- c. G PULLlN 2,303,707

ROOT MOUNTING FOR ROTOR BLADES I Filed Jap. 18, 1940 3 Sheets-Sheet 1 I III ML/Lg,

ATTORNEYS .Dec. 1, 1942. c. G. PULLIN ROOT MOUNTING FOR BLADES Filed Jan. l8, 1940 3 Sheets-Sheet 2 hbx QTQLQ axim xy mQ v5 Dec. 1, 1942. c. G. PULLIN ROOT MOUNTING FOR ROTOR BLADES Filed Jan. 18, 1940 3 Sheets-Sheet 3 INVENTOR ATTOR 5Y5 WJMM Patented Dec. 1, 1942 ROOT MOUNTING FOR ROTOR BLADES Cyril George Pullin, Genista, Newton Mearns, Scotland, assignor to Autoglro Company of America, Willow Delaware Grove, Pa., a corporation of Application January 18, 1940, Serial No. 314,421 In Great Britain December 31, 1938 4 Claims.

The present invention relates to root mountings for rotor blades, an object of the invention being to provide a root mounting in which peripheral compression of the root portion of the spar increases with increase of tension in the spar due to centrifugal force.

According to the present invention the spar is provided at its root end with a truncated conical portion, the larger end of which is at the extreme root end and is surrounded by a metal root socket in the form of an elongated truncated cone which fits over the conical portion of the spar and is flanged or screw-threaded externally near its larger end to permit of attachment to the rotor hub or to a link or other part associated therewith.

The conical root end of the spar may be integral with the main spar of the rotor blade or may consist partly of a member integral with said main spar and partly of a wedge-shaped member secured thereto. If desired, the root end may be hollow. In this case it is advantageously provided with an internal reinforcing member to increase its resistance to inward compression.

Several forms of construction in accordance with this invention are illustrated by way of example in the accompanying drawings, in which:

Fig. 1 is a plan view partly in section of one form;

Fig. 2 is an elevational view of the form shown in Fig. 1 but with the socket removed;

Fig. 3 is a sectional view on the line III-HI of Fig. 1;

Fig. 4 is a sectional view on the line IV-IV of Fi 1;

Figs. 5 to show a modification, Fig. 5 being a plan view, Fig. 6 an elevational view and Figs. 7, 8, 9 and 10 sectional views on the lines VII, VII[, 11! and X of Fig. 5 respectively;

Further alternative constructions are shown in sectional elevation in Figs. 11 and 12, 13 and 14, and 15 and 16, Figs. 12, 14 and 16 being sectional views on th lines XII-X11, XIV-XIV and XVIXVI of Figs. 11, 13 and 15 respectively.

Referring to Figs. 1 to 4: a rotor blade has a main spar I 00 which, as shown in Fig. 4, lies adjacent the leading edge-of the blade and has surfaces IOI, I02 which form part of the surface of the blade. has a dovetail I 03 which extends along its length and onto which a leading edge weight I04 is secured. This weight keeps the sectional center of gravity of the blade well forward, which, as is already known in the art of rotary winged air At its leading edge the spar I00 craft, is aerodynamically beneficial. Advantageously a ductile metal is used for this leading edge weight to enable it to be rolled onto the dovetail I03. Adjacent its rear edge the spar I00 has checked out portions I05, I06 on its lower and upper surfaces respectively which accommodate the leading edge of sheets of plywood I01, I08 which form the main part of the blade surface. Cross bracing members such as I09 and H0 are provided in the interior of the part of the blade covered by the plywood sheets I01, I08.

As shown in Fig. 1, the main spar I00 is altered in form at its extreme root end which is in the form of one half of a truncated cone III (see especially Fig. 3). Secured to the main spar I00 at its extreme root end is an auxiliary wedgeshaped member II2 which completes the conical form of the root end of the blade andwhich may extend some distance along the blade to assist in withstanding shear and bending moments in the blade. The auxiliary member II2 may be secured in any desired way to the spar I00 and its root end III, but advantageously it is secured by glueing or by glueing in addition to other securing means.

Preferably the spar I00 and. wedge-shaped member H2 are built up of wood laminations which may run vertically or horizontally along the length of the blade. These laminations may be compressed in dies and be secured together by synthetic resin adhesives.

Surrounding the extreme root end II I of the spar I00 and the auxiliary member H2 is a metal sleeve II 3 in the form of an elongated truncated cone. The sleeve is passed over the main spar I00 from its tip end before the auxiliary member H2 is secured thereto. The auxiliary member H2 is then inserted into the sleeve II3 from the root end and secured in position on the spar I00. Before the glue between the spar I00 and the auxiliary member I I2 has set, the sleeve H3 is moved axially so as to exert an inward pressure on the extreme root end, this axial pressure being obtained by a pre-loading device (not shown) which presses against the root end of the blade spar and the auxiliary member I I2. Advantageously an adhesive such as a thermoplastic synthetic resin is introduced between the sleeve and the root end and in addition a moisture-excluding ring II4 may be heldin a recess H5 at the narrower end of the sleeve H3.

The sleeve H3 and the root end of the spar and auxiliary member are apertured at H6 and Ill adjacent the extreme root end for an eye bolt H8 which extends transversely across the ing through the sleeve and the root of the spar prevents relative rotation between them and is held in position by a screw nut H9 at the trailing edge of the spar. At the leading edge the end of the eye bolt H6 is forked, as shown in Fig. 3, the two arms I26 of the fork having holes 1 I2I through which a split pin I22 may be passed. A rod I23, which is a continuation of the leading edge weight I64 towards the root end of the blade, has at its end a screw-threaded part I26 which passes through the space enclosed by the arms I26 of the eye bolt and the split pin I22 and is held in position by a screw nut I25. The centrifugal force acting on the leading edge weight I64 is transmitted by the rod I23 and screw nut I25 to the eye bolt H8 and thence to the-sleeve II3 near its root end, thus relieving the spar of this load.

In the alternative construction shown in Figs. to 10, the extreme root end of the blade is hollow. The main spar I56, which is built up of lengthwise wooden laminations in a horizontal or vertical plane, has at its leading edge a dovetail I5I to which is secured a leading edge weight I52 and recesses I53 and 154 at its trailing edge for receiving the plywood blade covering indicated in chain dotted lines at I55. The spar is increased in thickness towards the root end by the addition of circumferential laminations which are wrapped round the spar. These circumferential laminations are arranged to give the extreme root end of the spar a truncated conical shape as indicated at I56, the greatest width or thickness of the spar being at the root end.

A metal sleeve I51 of truncated conical form is threaded over the spar I56 from its tip end and passes along the spar to the root end where it surrounds the conical part I56 of the spar and exerts an inward pressure thereon, this pressure being obtained during manufacture by apre-loading device (not shown). when the sleeve I51 is in position on the outside of the conical part I56, the interior of the root end is bored out, as shown at I56, and a metal liner I59 is inserted within this bored out portion. The liner I59 is pressed into the root end of the blade by a ring I66 having an external screw-thread which engages an internal screw thread I6I at the root end of the sleeve I51. The material of the root end of the spar is thus compressed between the sleeve I51 and the liner I59. If

desired, a suitable adhesive such as a thermoplastic synthetic resin may be interposed between the sleeve I51 and the liner I59 and the root end of the spar. The ingress of moisture may be prevented by a ring I62 of rubber or other material housed in a recess I63 at the smaller end of the sleeve I51.

The leadging edge weight I52 is extended towards the root end of the blade by a rod I64 secured by a screw nut I65 to an eye bolt I66 which passes transversely through the root end of the sleeve I51, the. spar I56 and the liner I 59, whichare apertured for this purpose. The eye bolt I66 is secured in position by a screw nut I61 and may be provided with lightening holes such as I66. The general arrangement of the eye bolt and rod I64 is similar to thatshown in Figs. 1 and 3.

In the construction shown in Figs. 11 to a hollow spar is used.

1 Referring to Figs. 11 and 12: a hollow spar the blade nearer the leading edge.

. of the spar.

m is wan. miss d in diam ter. a lm-'- cated at 26I, at itsiroot 'end andthispart-jfl is 'surrounded by a metal 'sleeve 262;. provided with a screw thread 263 fforjattachment to l rotor hub member. Within the-conical part2" oi the spar is a reinforcing member. 264 which is hollowed out conically, as indicated at 26.5. and which has a part 266 which extends a short distance outwardly within the spar 266. The conical part 26I of the spar is compressed between the liner 262 and the reinforcing member 264 and is advantageously secured to these parts by an adhesive such as a thermo-plastlc synthetic resin.

At its leading and trailing edges the spar 266 has flanges 261 and 268. The spar 266 is built up to a generally oval shape by the addition of strips of material 269 and 2I6 on each side of' the flanges 261 and 268 respectively. Advantageously the material 269 is comparatively heavy so as to bring the centre of gravity of the spar towards the leading edge of the blade. For example compressed wood of a specific gravity of about 1.36 may be used for the strips 269 while a somewhat lighter material is used for the strips 2I6.

In the construction illustrated in Figs. 13 and 14, the main. spar 256 has at its leading edge an external flange 25I which extends along its length. The spar 256 is of ovoid form. At its root end the spar is enlarged conically, this enlarged part being clamped between a sleeve.252 and an inner reinforcing member 253 which maintain the root portion 254 under compression. Secured to the leading edge of the spar are strips 255 of comparatively heavy material which' tend to bring the centre of gravity of The sleeve 252 has an external screw thread 256 at its root end for attachment to a hub member.

In Figs. 15 and 168. further alternative construction is illustrated. The spar 366 of oval section has secured within it along its leading edge a weight 36I which extends along the length Some distance from the root end of the spar the cross section is changed from oval to circular and from this point towards the root end the diameter increases to form a conical part 362 which is clamped between a sleeve 363 and an inner reinforcing member 364. This reinforcing. member 364 extends to the point at whichthe cross section of the spar changes and is hollowed out as indicated at 365 at the root end. An external screw thread 366 is provided at the root end of the sleeve for attachment to a hub member.

The spars shown in Figs. 11 to 16 are preferably made of improved wood, that is to say wood laminations secured together under pressure with a thermo-plastic synthetic resin. This form of construction allows the spars to be made accurately and reduces errors due to distortion which are prevalent in metal hollow spars. With improved wooden'spars, the accuracy of the spar is What I claim is:

1. A blade for an aircraft sustaining rotor, including a spar having root end attachment means tapered to its greatest size at the extreme root, an elongated tapered sleeve fitted on said portion and an elongated member of relatively high specific gravity extended throughout a major portion of theblade length, said member being supported by said spar and substantially paralleling the spar axis in a zone adjacent the leading side thereof, and further being supported against the action of centrifugal force by connection to said tapered root end attachment means, thereby substantially eliminating bending of the spar due to the action of centrifugal force on the elongated member.

2. A blade for an aircraft sustaining rotor, including a spar having root end attachment means tapered to its greatest size at the extreme root; an elongated tapered sleeve fitted on said portion and an elongated member of relatively high specific gravity extended throughout a major portion of the blade length, said member being supported by said spar and substantially paralleling the spar axis in a zone adjacent the leading side thereof, and further being supported against the action of centrifugal force by connection to anchor means extended transversely through th root end of the spar and sleeve.

3. A blade for an aircraft sustaining rotor, including a spar having a member of relatively high specific gravity extended throughout a major portion of the blade length supported by said spar, said member substantially parallelling the spar axis in a zone adjacent the leading side thereof, the spar having a dovetail recessf formed along its leading edge, and the extended member being of ductile material rolled into said dovetail.

4. A blade for an aircraft sustaining rotor, including aspar having hollow root end attachment means tapered to its greatest size at the extreme root, cooperating internal and external tapered members between which the tapered attachment means is compressed, external flanges extended along the leading and trailing edge of said spar, contour-forming material of relatively high specific gravity built up adjacent the leading side of the spar and supported by the leading flange, contour-forming material of a lower specific gravity built up adjacent the trailing side of the spar and supported by the trailing flange, said flanges further being extended into adjacent the compression zone between said tapered members, thereby to reinforce said spar against bending moments.

CYRIL GEORGE P. 

